The present invention relates to the field of environmental remediation and 5 specifically to the remediation of pollutants in contaminated soil. More specifically the instant invention provides a method for the remediation of toxic compounds from soil whereby the contaminated soil is stabilized in the presence of a pollutant degradative agent.
Soil and groundwater pollution is a worldwide problem associated primarily with government and industrial sites where mishandling or improper disposal of chemicals has brought a variety of pollutants in contact with the soil. Common pollutants include hydrocarbons, heavy metals, and halogenated volatile organic solvents such as tetra-, tri-, or di- chloroethylene, carbon tetrachloride, chloroform and methylene chloride. The toxicology of many organic solvents suggests that these compounds may be carcinogenic and damaging to specific organs such as the liver and kidneys (Price, P. S., Memo of the U.S. Environmental Protection Agency, Office of Water, Washington, D.C. (1985); Vogel, T. Ni, Environ. Sci. Technol. 21, 722, (1987).
Many of the most troublesome solvents fall into the category of dense non-aqueous phase liquids (DNAPLs). The remediation of DNAPLs is problematic since, their high density and low water solubility cause them to sink through the soil and water thereby contaminating successive levels, and follow topographic lows within an aquifer system often accumulating atop the underlying clay stratum. Further, since most are sparingly soluble in water they are adsorbed on to soil particles producing tenacious underground plumes of dissolved organic which cannot be readily and permanently removed by standard pump and treat technology (Biswas,. N., et al., Water Environ. Res. 64,170,10,1(992); Hutter, G. M., et al., Water Environ. Res. 64, 69, (1992)).
Current methods for remediation of DNAPLs include excavation, slurry walls, cutoff trenches, in-situ biodegradation and pump and treat. Because of the pervasive nature of DNAPL contamination a common approach to remediation has been to treat the DNAPL contaminated groundwater plume as opposed to addressing the source of contamination. One successful method for groundwater plume treatment involves the use of zero valent metals. For example, Matheson et al., (Environ. Sci. Technol., 28, 2045, (1994)) disclose a method for the reduction of chlorinated solvents by fine-grained iron metal in a well-mixed anaerobic batch system. Similarly R. Gillham (U.S. Pat. No. 5,266,213) teaches a method for the decontamination of chlorinated solvents from a groundwater plume where the contaminated groundwater is fed through a trench containing iron filings under strict exclusion of oxygen and under highly reducing conditions. Finally, Sweeny et al., (U.S. Pat. No. 3,640,821) teach that halogenated organic pesticides, typified by DDT, chlordane, lindane and the like that are typically near the surface and strongly absorbed on soils, may be degraded by reacting them with metallic zinc under mildly acid conditions (U.S. Pat. No. 3,640,82 1) or by metallic couples such as iron and copper (U.S. Pat. No. 3,737,384).
The above methods are useful for the treatment of dissolved groundwater plumes but do not address how the source of DNAPL contamination may be remediated in-situ.
Methods of treating soil contamination with elemental metals are known. For example, Cutshall et al., (U.S. Pat. No. 5,197,823) discloses a method for treating polychlorinated biphenyl (PCB) contaminated soils by adding an effective amount of elemental zinc powder to moistened soil. In similar fashion Butler et al., (J Environ Sci Health Part B Pestic Food Contam Agric Wastes 16, 95, (1998)) disclose the reductive dechlorination of dieldrin and endrin in soil samples containing powdered zinc metal in combination with acetic acid and acetone to facilitate the reaction.
These methods of treating soils are useful, but cannot be applied to DNAPL source treatment. An effective method of deactivating the source of DNAPL contamination is by reducing the permeability of the contaminated region to water flow. This is typically done through the use of stabilizing agents. Stabilizing reagents can be selected or designed to greatly reduce the permeability of the soil, thereby diverting groundwater around a contaminated area, thereby preventing fin-ther leaching into the groundwater. Stabilizing agents also function to a reduce the hazard of a waste by binding and converting the contaminants into a less soluble, less mobile or less toxic forms. Typical stabilization reagents include Portland cement, metal oxides, clays, natural materials (peat moss, natural zeolites, vermiculite, etc.), synthetic materials (zeolites, fly ash, organic polymers, etc.), and activated carbon. (Conner, J. R., Chemical Fixation and Solidification of Hazardous Wastes, Van Nostrand Reinhold, II 5 Fifth Avenue, New York, N.Y., 10003, (1990)).
Although stabilization technologies are now widely used for treatment of hazardous waste sludge, power plant residues, municipal ashes, nuclear wastes, and contaminated soils, these processes have shortcomings for organic contaminants, including the difficulty in demonstrating the long-term stability of the treated waste and the fact that the contaminants are not destroyed or degraded.
The problem to be overcome therefore is to develop a method that will chemically attack the source organic DNAPL""s in the soil and effectively prevent the contaminant from migrating in the groundwater. Applicants have solved this problem by developing a method that combines the use of stabilization technology to reduce water permeability at the contamination source and a degradative agent that facilitates the destruction of the organic contaminant in its stabilized form. Although both elements of this method have been practiced separately, applicants are the first to teach how to combine the two technologies such that the two are operable in concert. Applicant""s method reduces the permeability at the contamination source by adding/mixing a stabilizing agent such as cement, bentonite clay or iron chloride with a degradative agent. such as elemental iron, 10 metal couples or a base catalyzing decomposition agent. Introduction of the combined stabilizing agent/degradative agent into a contaminated area results in the diverting of the majority of groundwater flow around the source volume (thus preventing leaching into the groundwater) while at the same time binding and destroying the contaminant.
The present invention concerns a process for the chemical degradation and stabilization of chemical pollutants at a contamination source in a soil contaminated with pollutants comprising admixing with the soil at said contamination source an effective amount of degradative reagent and a suitable stabilizing agent to form a stabilized degradative reagent such that said admixing results in the reduction of permeability at said contamination source, diversion of groundwater around the contamination source, and the degradation of said pollutant over time. Further provided is a process for the metal initiated chemical degradation of halogenated organic compounds from soil contaminated with halogenated organic compounds comprising admixing with said contaminated sod an effective amount of a metallic couple comprising a reductive zero valent metal and a metal catalyst, an effective amount of ferrous iron and alkaline buffer, or an effective amount of an alkali metal sulfide or polysulfide, wherein said metallic couple, buffered ferrous iron, or sulfide dehalogenates said halogenated organic compounds to lower the concentration of said halogenated organic compounds in soil.